You may not even get protection against the intended virus. Why? First, because viruses change over time. The piece that was in the vaccine may not ‘look’ the same (chemically) as the real thing (months later, after all!). Second, the vaccine may not have given you enough stimulation to fight off the disease.
The Centers for Disease Control (CDC) is looking at whether or not the flu vaccine is effective. Preliminary results indicate you’ll get just as sick (with colds, flu, flu-like illnesses) if you got the vaccine than if you didn’t. Why doesn’t the vaccine work? In order to understand the answer, you’ll need to understand some specifics about the flu vaccine and a bit about how immunity works.
Flu Vaccine Facts
There is no single virus that causes the flu; there is no one flu vaccine that protects against all of them. A flu vaccine is designed to confer immunity against the strains of flu that are expected to be most common and most serious. The vaccine is a sort of one-size-fits-all solution, even though there are more types of flu than covered by the vaccine and the flu types vary according to region. It takes time to produce vaccines, so a new vaccine can’t be instantly produced when a new type of flu starts to cause problems.
The Vaccine and Immunity
The flu vaccine gives your body parts of inactivated flu viruses. These virus parts correspond to parts of proteins floating around in your body. When the virus part contacts a chemical ‘match’, it stimulates the body to produce the cells and antibodies that can remove this particular intruder. Antibodies are proteins that float in body fluids and can bind to specific chemical markers. When an antibody binds to a substance, it essentially marks it for destruction by other cells. However, an antibody for one type of flu won’t necessarily bind to a virus part from another type of flu. You don’t get protection against other viruses. A flu vaccine can only stimulate your immune system to protect you against the viruses in the vaccine, with some lesser protection against very similar ones.